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Thread: Randomizing after skip

  1. #1
    Join Date
    Apr 2007
    Posts
    2

    Randomizing after skip

    I have a questionnaire with 20 trials that need to be presented in random order. The subject has a choice of two buttons to click, one of which indicates the target letter displayed in the trial. Once the subject responds, it skips to either a “correct” or “incorrect” instruction line. I have not been able to find a way to get the other 19 stimuli to present in random order. Any ideas?
    Last edited by jarvis24; 04-26-2007 at 06:17 AM. Reason: additional info

  2. #2
    Join Date
    Nov 2005
    Posts
    3,313
    One way you could do this is to follow each trial with a correct and incorrect item. Treat the three items as a single set by assigning each of the three the same BGR value. That way all the sets will occur in a random order, but the items within sets will be fixed. You can easily define whether the subject gets incorrect or correct feedback. Say you have q15, q15c, q15i. If they respond correctly to q15, then they go on to q15c and otherwise they skip q15c and go to q15i.

    The only problem, in this example, occurs when they get the item correct and go to q15c. If the next item is q15i (the incorrect feedback), then they need to be skipped over that. But you have randomized the sets so you do not know in advance what the next set will be, so you don't have a variable name! This is what you can do:

    As of v2006.1.31, instead of having to explicitly name the variable you want to skip to, you can simply enter +1, +2, +3, +n, etc. items. MediaLab will automatically skip that many items without needing to know the name of a "skipto" variable--it will simply resume wherever it ends up. This is especially nice when the item being skipped to might be randomly determined.

    So in the example above, you could simply use a skipto value of +1 for q15c and it would simply skip the incorrect feedback and go straight to the next set.

    Sounds a little complicated but it's actually pretty simple in execution. Let me know if you have any trouble with it.
    Last edited by jarvis24; 04-27-2007 at 08:45 AM.

  3. #3
    Join Date
    Oct 2008
    Posts
    33
    Hello, hope it's okay to bring up an older thread. I am trying to do something very similar and ran across this one.

    Anyways, participants are rating photos of people. The photos are presented in random order. The participant is asked, "Is this person wearing glasses?" and they must choose yes or no. If yes, I want them to go to a fill in the blank item where they describe the glasses. If no, I want it to skip this fill in the blank item.

    I tried giving both questions for the same photo the same BGR value, and when the participant chooses "yes", the skip value is "none" (so it should go on to the next question, the fill in the blank item, right?) and when the participant chooses "no" the skip value is +1 (I was hoping this would bring it to another randomly selected photo to ask "Is this person wearing glasses".)

    The problem is that when you actually run the presentation and click "no," it just ends the experiment rather than going on to the next photo.

    I also tried reversing the order of the scale response choices so that "no" is first and "yes" is second, but it didn't make a difference.

    Any idea what's going wrong here?

    Thank you.

  4. #4
    Join Date
    Oct 2008
    Posts
    33
    Update: I got my design to work by adding a blank, one second duration instruction page and skipping to that, which is an idea I got from another thread on the forum.

    I'm still curious though, if someone gets a chance to respond, why the +1 thing wasn't working for me. Thanks!

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